Hydrogen sulfide is synthesized in the gills of the clam Mercenaria mercenaria and acts seasonally to modulate branchial muscle contraction

Biochemical and behavioral effects of zinc oxide nanorods on the freshwater mussel Potomida littoralis

Our study aimed to investigate the impact of nano-zinc oxide (nZnO), a widely used pollutant in industry, pharmaceuticals, and personal care products, on the behavior and oxidative stress of freshwater mussels (Potomida littoralis) an indicator species and also a model non-target organism in ecotoxicology. To this end mussels were exposed to nZnO (50 and 100 µg/L) and Zn2+ from ZnSO4 (50 and 100 µg/L) for 7 days. ZnSO4 was used for comparison purposes and to determine if the toxicity of nZnO was due to the release of ions into the aquatic environment. We evaluated changes in oxidative stress markers, including catalase (CAT), glutathione-S-transferase (GST), acetylcholinesterase (AChE), and malondialdehyde (MDA) levels, on the mussel gills and digestive glands. Additionally, the effect of nZnO on the filtration rate of bivalves was studied. The findings showed that the mussel tissue's different parameters were significantly affected by exposure to various concentrations of nZnO, causing changes in their behavior that led to a decrease in filtration rate. Additionally, noteworthy increments were observed in CAT activity, AChE activity, and MDA levels, whereas GST activity displayed a decreasing trend, implying that oxidative stress contributes to the toxicity of nZnO. The purpose of this review is to present a framework for comprehending the toxicological impacts of nanoparticles from an environmental standpoint. Additionally, it includes novel information about the connections between nanoparticles (NPs) and bivalve species.

Mitochondrial Mechanisms Underlying Tolerance to Fluctuating Oxygen Conditions: Lessons from Hypoxia-Tolerant Organisms

Oxygen (O2) is essential for most metazoan life due to its central role in mitochondrial oxidative phosphorylation (OXPHOS), which generates >90% of the cellular adenosine triphosphate. O2 fluctuations are an ultimate mitochondrial stressor resulting in mitochondrial damage, energy deficiency, and cell death. This work provides an overview of the known and putative mechanisms involved in mitochondrial tolerance to fluctuating O2 conditions in hypoxia-tolerant organisms including aquatic and terrestrial vertebrates and invertebrates. Mechanisms of regulation of the mitochondrial OXPHOS and electron transport system (ETS) (including alternative oxidases), sulphide tolerance, regulation of redox status and mitochondrial quality control, and the potential role of hypoxia-inducible factor (HIF) in mitochondrial tolerance to hypoxia are discussed. Mitochondrial phenotypes of distantly related animal species reveal common features including conservation and/or anticipatory upregulation of ETS capacity, suppression of reactive oxygen species (ROS)-producing electron flux through ubiquinone, reversible suppression of OXPHOS activity, and investment into the mitochondrial quality control mechanisms. Despite the putative importance of oxidative stress in adaptations to hypoxia, establishing the link between hypoxia tolerance and mitochondrial redox mechanisms is complicated by the difficulties of establishing the species-specific concentration thresholds above which the damaging effects of ROS outweigh their potentially adaptive signaling function. The key gaps in our knowledge about the potential mechanisms of mitochondrial tolerance to hypoxia include regulation of mitochondrial biogenesis and fusion/fission dynamics, and HIF-dependent metabolic regulation that require further investigation in hypoxia-tolerant species. Future physiological, molecular and genetic studies of mitochondrial responses to hypoxia, and reoxygenation in phylogenetically diverse hypoxia-tolerant species could reveal novel solutions to the ubiquitous and metabolically severe problem of O2 deficiency and would have important implications for understanding the evolution of hypoxia tolerance and the potential mitigation of pathological states caused by O2 fluctuations.

Metal accumulation, biochemical and behavioral responses on the Mediterranean clams Ruditapes decussatus exposed to two photocatalyst nanocomposites (TiO2 NPs and AuTiO2NPs)

Nanoparticle decoration with noble metal represents a promising alternative to improve their photocatalytic and photovoltaic properties. However, toxicity can be influenced by such modification, as the bioavailability of these substances may be influenced. To understand how decoration influences the NP impacts in marine ecosystems, we exposed suspension-feeding clams, Ruditapes decussatus, to two photocatalyst nanocomposites, TiO₂ NPs and AuTiO₂ NPs, over 2 concentrations, 50 μg L^-1and 100 μg L^-1, in a laboratory experiment. Accumulation of Au and Ti in gills and digestive gland was noted in clams after exposure to TiO₂ NPs and AuTiO₂ NPs using inductively coupled plasma optic emission spectroscopy (ICP-OES). TiO₂ and AuTiO₂ NPs alter the behavior of the clams Ruditapes decussatus by reducing filtration and respiration rates. Furthermore, the highest concentration of TiO₂NPs induces an overproduction of H₂O₂ in gills and digestive gland and NO production only in gills. Superoxide dismutase (SOD), Catalase (CAT), Glutathione-S-transferase (GST) and acetylcholinesterase (AChE) activities were induced in gills and digestives gland in concentration and nanocomposite type dependent manner. Decorated form presented higher Malondialdehyde (MDA) levels in gills and digestive gland than the undecorated form, suggesting different mechanisms of action that may be mediated through oxidative stress. In conclusion, the considered parameters could represent reliable biomarkers for the assessment of NP toxicity on R. decussatus as biological biomonitoring model. In addition, based on the obtained results, nanoparticle decoration influences the toxicity of metal nanoparticles in marine organism.

A novel role of sONE/NOS3/NO signaling cascade in mediating hydrogen sulphide bilateral effects on triple negative breast cancer progression

Hydrogen sulphide (H₂S) gas has been recognized as an intracellular mediator influencing an array of signaling pathways. Yet, the role of H₂S in cancer progression has been controversial. This study aims to unravel the role of exogenous H₂S in triple negative breast cancer (TNBC) and to further investigate any possible association of H₂S mediated actions with the endogenous production of nitric oxide (NO) gas. A wide concentration range of NaHS (20-2000 μM) and a variable reaction time (2-72 h) were probed. A bell-shaped impact of H₂S on TNBC cellular viability, proliferation, migration, invasion and colony forming ability was repeatedly observed in the aggressive TNBC cell lines, MDA-MB-231 but not in hormone receptor positive, MCF-7 cells. This bell-shaped effect was found to be shifted towards the left upon increasing the reaction time within the range of 2-24 h. However, this was totally opposed in case of continuous exposure (72 h) to exogenous H₂S. An inverted bell-shaped effect of H₂S on TNBC cellular growth, migration, proliferation and colony forming ability was shown. Moreover, this study provided the first evidence of a possible involvement of NO in mediating H₂S actions in TNBC. Such intricate cross-talk was found to be orchestrated by the novel lncRNA, sONE and its down-stream target NOS3 building up a novel axis, sONE/NOS3/NO, that was shown to play a pivotal role in plotting the bilateral effect of H₂S on TNBC progression. Finally, this study showed that low and continuous exposure of H₂S serves as a novel, selective and effective strategy in harnessing TNBC oncogenic profile through cGMP dependent and independent pathways where alterations of cell cycle regulatory proteins such as TP53 and c-Myc was observed. Moreover, NaHS could repress TNBC migration and invasion capacities through repressing the intracellular adhesion molecule, ICAM-1. In conclusion, this study provides an insight about the role of exogenous H₂S in TNBC cell lines highlighting a novel crosstalk between H₂S and NO orchestrated by sONE/NOS3 axis.

Transcriptomic responses to extreme low salinity among locally adapted populations of Olympia oyster (Ostrea lurida)

The Olympia oyster (Ostrea lurida) is a foundation species inhabiting estuaries along the North American west coast. In California estuaries, O. lurida is adapted to local salinity regimes and populations differ in low salinity tolerance. In this study, oysters from three California populations were reared for two generations in a laboratory common garden and subsequently exposed to low salinity seawater. Comparative transcriptomics was then used to understand species-level responses to hyposmotic stress and population-level mechanisms underlying divergent salinity tolerances. Gene expression patterns indicate Olympia oysters are sensitive to hyposmotic stress: All populations respond to low salinity by up-regulating transcripts indicative of protein unfolding, DNA damage and cell cycle arrest after sub-lethal exposure. Among O. lurida populations, transcriptomic profiles differed constitutively and in response to low salinity. Despite two generations in common-garden conditions, transcripts encoding apoptosis modulators were constitutively expressed at significantly different levels in the most tolerant population. Expression of cell death regulators may facilitate cell fate decisions when salinity declines. Following low salinity exposure, oysters from the more tolerant population expressed a small number of mRNAs at significantly higher levels than less tolerant populations. Proteins encoded by these transcripts regulate ciliary activity within the mantle cavity and may function to prolong valve closure and reduce mortality in low salinity seawater. Collectively, gene expression patterns suggest sub-lethal impacts of hyposmotic stress in Olympia oysters are considerable and that even oysters with greater low salinity tolerance may be vulnerable to future freshwater flooding events.

Role of Nitric Oxide in the Cardiovascular and Renal Systems

The gasotransmitters are a family of gaseous signaling molecules which are produced endogenously and act at specific receptors to play imperative roles in physiologic and pathophysiologic processes. As a well-known gasotransmitter along with hydrogen sulfide and carbon monoxide, nitric oxide (NO) has earned repute as a potent vasodilator also known as endothelium-derived vasorelaxant factor (EDRF). NO has been studied in greater detail, from its synthesis and mechanism of action to its physiologic, pathologic, and pharmacologic roles in different disease states. Different animal models have been applied to investigate the beneficial effects of NO as an antihypertensive, renoprotective, and antihypertrophic agent. NO and its interaction with different systems like the renin–angiotensin system, sympathetic nervous system, and other gaseous transmitters like hydrogen sulfide are also well studied. However, links that appear to exist between the endocannabinoid (EC) and NO systems remain to be fully explored. Experimental approaches using modulators of its synthesis including substrate, donors, and inhibitors of the synthesis of NO will be useful for establishing the relationship between the NO and EC systems in the cardiovascular and renal systems. Being a potent vasodilator, NO may be unique among therapeutic options for management of hypertension and resulting renal disease and left ventricular hypertrophy. Inclusion of NO modulators in clinical practice may be useful not only as curatives for particular diseases but also for arresting disease prognoses through its interactions with other systems.

Neuroenzymatic activity and physiological energetics in Manila clam, Ruditapes philippinarum, during short-term sublethal exposure to harmful alga, Heterocapsa circularisquama

The harmful alga, Heterocapsa circularisquama, causes recurrent mortalities of bivalve molluscs in Japan, with demonstrated hemolysis and cytotoxicity in rabbit erythrocytes, HeLa cells, and bivalve tissues. Nonetheless, the effects of exposure to sublethal cell densities on the physiological energetics of bivalves have not been investigated, nor the potential involvement of neurotoxicity. In the present study, two sets of experiments were conducted with adult clams, Ruditapes philippinarum. In the first set, the clearance rate (CR), respiration rate (RR), absorption efficiency (AE), ingestion rate (IR), and absorption rate (AR) were examined in clams exposed to H. circularisquama to quantify the scope for growth (SFG) as an indicative of the bioenergetic status of clams (5, 50, 2.5×10(2), and 5×10(2)cellsml(-1); under 15°C and 20°C). In the second set, the activity of the biomarker of neurotoxic exposure, acetylcholinesterase (AChE), was monitored following 3, 6, 24, and 48h of exposure (5, 50, 5×10(2), and 10(3)cellsml(-1), at 20°C) in gills of R. philippinarum, and compared to that in Mediterranean mussels, Mytilus galloprovincialis; a species also affected by H. circualrisquama and in which AChE activity was more extensively studied. At 15°C, CR, IR, and AR were decreased for exposures to 50-5×10(2) cells ml(-1) resulting in a significant decrease in the absorbed energy (A), and a significant decrease in SFG at 5×10(2)cellsml(-1). At 20°C, AE was null for exposures to 2.5×10(2) and 5×10(2)cellsml(-1). RR was decreased at 2.5×10(2) and 5×10(2)cellsml(-1), CR, IR, and AR were decreased at 5-5×10(2)cellsml(-1), and the AE was null for 2.5×10(2)-5×10(2)cellsml(-1) resulting in a significant decrease in the respired energy (R), but mainly in (A) especially at 2.5×10(2) and 5×10(2)cellsml(-1) decreasing the SFG over the entire range of cell density with negative values for 2.5×10(2) and 5×10(2)cellsml(-1). The activity of AChE in both clams and mussels was significantly reduced following 3-48h of exposure to 5-5×10(2)cellsml(-1). Reduction in the energy available for clams to grow and reproduce was induced mainly via decreased energy acquisition, and delayed and/or reduced functions of the digestive organs. In addition, this is the first report of decreased neuroenzymatic activity in two bivalve molluscs induced by exposure to H. circularisquama potentially via either neurotoxic compounds affecting the activity of gill cilia and/or gill muscles, and/or potentially via either neurotoxic compounds affecting the activity of gill cilia and/or gill muscles, and/or non-cholinergic affects associated with other functions; both resulting in decreased SFG. The relationship between the decreased AChE and decreased SFG should be corroborated in future research.

Modulation of pumping rate by two species of marine bivalve molluscs in response to neurotransmitters: Comparison of in vitro and in vivo results

Most studies regarding the neuroanatomy and neurophysiology of molluscan ctenidia have focused on isolated ctenidial tissue preparations. This study investigated how bivalve molluscs modulate their feeding rates by examining the effects of a variety of neurotransmitters, including serotonin, dopamine, and the dopamine agonist apomorphine on both isolated ctenidial tissue and in intact members of two commercially important bivalve species: the blue mussel, Mytilus edulis; and the bay scallop Argopecten irradians. In particular, we examined the effect of changes in: 1) beat of the lateral cilia (in vitro), 2) distance between ctenidial filaments and/or plicae (in vivo), and 3) diameter of the siphonal openings (in vivo) on alteration of bulk water flow through the mantle cavity. Important differences were found between isolated tissue and whole animals, and between species. Drugs that stimulated ciliary beat in vitro did not increase water processing rate in vivo. None of the treatments increased water flow through the mantle cavity of intact animals. Results suggest that A. irradians was primarily modulating lateral ciliary activity, while M. edulis appeared to have a number of ways to control water processing activity, signifying that the two species may have different compensatory and regulatory mechanisms controlling feeding activity.

Role of cGMP in hydrogen sulfide signaling

The importance of hydrogen sulfide (H2S) in physiology and disease is being increasingly recognized in recent years. Unlike nitric oxide (NO) that signals mainly through soluble guanyl cyclase (sGC)/cGMP, H2S is more promiscuous, affecting multiple pathways. It interacts with ion channels, enzymes, transcription factors and receptors. It was originally reported that H2S does not alter the levels of cyclic nucleotides. More recent publications, however, have shown increases in intracellular cGMP following exposure of cells or tissues to exogenously administered or endogenously produced H2S. Herein, we discuss the evidence for the participation of cGMP in H2S signaling and reconcile the seemingly divergent results presented in the literature on the role of this cyclic nucleotide in the biological actions of H2S.

The immunomodulation of inducible hydrogen sulfide in Pacific oyster Crassostrea gigas

Hydrogen sulfide (H2S) is an important gasotransmitter, which plays indispensable roles in cardiovascular, nervous and immune systems of vertebrates. However, the information about the immunomodulation of H2S in invertebrates is still very limited. In the present study, the temporal expression profile of cystathionine γ lyase in oyster Crassostrea gigas (CgCSE) was investigated after the oysters were stimulated by lipopolysaccharide. The expression levels of CgCSE mRNA transcripts in hemocytes increased significantly at 12h (1.31-fold of the PBS group, P<0.05) after LPS stimulation. The immunomodulation of inducible H2S in oyster was examined by monitoring the alterations of both cellular and humoral immune parameters in response to the stimulations of LPS, LPS+Na2S and LPS+propargylglycine (PAG). The total hemocyte counts (THC) and hemolymph PO activity increased significantly after LPS stimulation, and the increase could be further enhanced by adding PAG, while inhibited by appending Na2S. The phagocytosis activity of hemocytes was also increased firstly after LPS treatment, and the increase was enhanced by adding Na2S but inhibited after appending PAG. The anti-bacterial activity in hemolymph increased at 3h post LPS treatment, and then decreased after adding PAG. The total SOD activity of hemolymph was also elevated at 6h post LPS treatment, and the elevated activity was depressed by adding Na2S. These results collectively indicated that H2S might play crucial roles in the immune response of oyster via modulating the turnover and phagocytosis of hemocytes, and regulating the anti-bacterial activity and proPO activation in the hemolymph.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

Screening of genes related to sulfide metabolism in Urechis unicinctus (Echiura, Urechidae) using suppression subtractive hybridization and cDNA microarray analysis

Exogenous sulfide can generally induce metabolic injuries in most organisms and even cause death. However, organisms inhabiting intertidal zones, hydrothermal vents, and cold seeps, can tolerate, metabolize, and utilize sulfide. In this study, both suppression subtractive hybridization and cDNA microarray analysis were employed to screen sulfide metabolism-related genes from the body wall in echiuran worm Urechis unicinctus, a marine sediment species. A total of 3456 monoclones were isolated and 82 were identified as differentially expressed genes in worms exposed to 50 μM sulfide for 24 h, compared to controls. The identified genes encoded proteins with multiple processes, including metabolism, cellular process, biological regulation, response to stimulus, multicellular organismal process, localization, development, and cellular component organization. Eight genes, serase, vacuolar protein, src tyrosine kinase, sulfide oxidase-like oxidoreductase, aprataxin, SN-RNP, aminopeptidase, and predicted protein, were selected to verify expression in the worm using qRT-PCR. The agreement of gene expression evaluation was 62.5% between the results of microarray analysis and qRT-PCR. These new data will provide clues for further probing of the molecular mechanism of sulfide metabolism.

The hydrogen sulfide signaling system: changes during aging and the benefits of caloric restriction

Hydrogen sulfide gas (H(2)S) is a putative signaling molecule that causes diverse effects in mammalian tissues including relaxation of blood vessels and regulation of perfusion in the liver, but the effects of aging on H(2)S signaling are unknown. Aging has negative impacts on the cardiovascular system. However, the liver is more resilient with age. Caloric restriction (CR) attenuates affects of age in many tissues. We hypothesized that the H(2)S signaling system is negatively affected by age in the vasculature but not in the liver, which is typically more resilient to age, and that a CR diet minimizes the age affect in the vasculature. To investigate this, we determined protein and mRNA expression of the H(2)S-producing enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), H(2)S production rates in the aorta and liver, and the contractile response of aortic rings to exogenous H(2)S. Tissue was collected from Fisher 344 × Brown Norway rats from 8-38 months of age, which had been maintained on an ad libitum (AL) or CR diet. The results demonstrate that age and diet have differential effects on the H(2)S signaling system in aorta and liver. The aorta showed a sizeable effect of both age and diet, whereas the liver only showed a sizeable effect of diet. Aortic rings showed increased contractile sensitivity to H(2)S and increased protein expression of CSE and CBS with age, consistent with a decrease in H(2)S concentration with age. CR appears to benefit CSE and CBS protein in both aorta and liver, potentially by reducing oxidative stress and ameliorating the negative effect of age on H(2)S concentration. Therefore, CR may help maintain the H(2)S signaling system during aging.

Review. Sulfur-containing volatile compounds in seafood: occurrence, odorant properties and mechanisms of formation

An inventory of the most part of sulfur-containing volatile compounds (SCVCs) present in seafood was carried out. These molecules constitute key compounds to understand and improve seafood quality. According to their nature, concentration and environmental parameters (temperature), they can move the overall seafood odor from desirable to rotten. Sulfury odors can also indicate problems in sanitary quality. Thus, it is essential to monitor the generation of these compounds to better control the organoleptic and sanitary quality of seafood. SCVC were divided in two categories: aliphatic compounds and cyclic compounds. Among cyclic SCVC, several families of compounds can be distinguished as thiophenes, thiazoles and their respective derivatives. The main pathways of formation of SCVC in seafood are investigated in order to better understand their presence in seafood aroma. Microbial mediated enzymatic reactions are mainly implied in the generation of aliphatic SCVC whereas Maillard reactions are involved in the generation of cyclic SCVC. A small part of SCVC could also derive from the environment by direct bioaccumulation of S-containing molecules or precursors. Then, the occurrence of SCVC in seafood is discussed according to the extraction methods, analysis methods - sometimes olfactometric methods and the species - the state and the average biochemical composition of the seafood matrix in which they were recovered. Finally, among the identified SCVC, the odorant properties of odor-active volatile compounds were investigated. Aromatic notes and odorant thresholds for odorant SCVC of seafood aroma are listed. Both pathways of formation and lists of SCVC linked to their odorant properties constitute important indicators to optimise seafood quality from an organoleptic and sanitary point of view.

Hydrogen sulfide induces oxidative damage to RNA and DNA in a sulfide-tolerant marine invertebrate

Hydrogen sulfide acts as an environmental toxin across a range of concentrations and as a cellular signaling molecule at very low concentrations. Despite its toxicity, many animals, including the mudflat polychaete Glycera dibranchiata, are periodically or continuously exposed to sulfide in their environment. We tested the hypothesis that a broad range of ecologically relevant sulfide concentrations induces oxidative stress and oxidative damage to RNA and DNA in G. dibranchiata. Coelomocytes exposed in vitro to sulfide (0-3 mmol L(-1) for 1 h) showed dose-dependent increases in oxidative stress (as 2',7'-dichlorofluorescein fluorescence) and superoxide production (as dihydroethidine fluorescence). Coelomocytes exposed in vitro to sulfide (up to 0.73 mmol L(-1) for 2 h) also acquired increased oxidative damage to RNA (detected as 8-oxo-7,8-dihydroguanosine) and DNA (detected as 8-oxo-7,8-dihydro-2'-deoxyguanosine). Worms exposed in vivo to sulfide (0-10 mmol L(-1) for 24 h) acquired elevated oxidative damage to RNA and DNA in both coelomocytes and body wall tissue. While the consequences of RNA and DNA oxidative damage are poorly understood, oxidatively damaged deoxyguanosine bases preferentially bind thymine, causing G-T transversions and potentially causing heritable point mutations. This suggests that sulfide can be an environmental mutagen in sulfide-tolerant invertebrates.

Seasonal control of particle clearance by isolated gills from the clam Mercenaria mercenaria

Pieces of gill isolated from the clam Mercenaria mercenaria clear colloidal graphite from seawater, and the clearance rates are measurable. 5-Hydroxytryptamine (5-HT) had a biphasic effect on clearance rates:concentrations from 10–6 to 10–5 mol l–1 5-HT increased clearance, but higher concentrations reduced it. During the summer, the gills were less responsive to 5-HT: the threshold increased from 1×10–6 to 5×10–6 mol l–1, and although the rate was still maximal at 10–5 mol l–1, it was significantly lower than the maximal rate in the winter. At 10–5 mol l–1 5-HT, which maximized clearance, the lateral cilia were active, the interfilament space decreased and the diameter of the water tubes increased. Higher concentrations of 5-HT contracted the gill musculature, which inhibited the lateral cilia, decreased the interfilament space even more and decreased the diameter of the water tubes. The nitric oxide (NO) generator DEANO stimulated clearance in the winter but had no effect during the summer. l-NAME, an inhibitor of NO synthesis, diminished the effect of 5-HT during the winter but was ineffective during the summer. The diminished response to 5-HT of winter gills treated with l-NAME was statistically equal to the response of the gills to 5-HT during the summer. Dopamine (DA) inhibited clearance, and the gills were more sensitive to DA in winter than in summer. Microscopic examination of untreated gills revealed little or no lateral ciliary activity,and clearance was minimal. Thus, clearance rates of isolated gills behave in a manner consistent with the seasonality and pharmacology of the lateral cilia and branchial musculature.

Mitochondrial depolarization following hydrogen sulfide exposure in erythrocytes from a sulfide-tolerant marine invertebrate

Sulfide-tolerant marine invertebrates employ a variety of mechanisms to detoxify sulfide once it has entered their bodies, but their integumentary,respiratory epithelium and circulatory cells may still be exposed to toxic sulfide concentrations. To investigate whether sulfide exposure is toxic to mitochondria of a sulfide-tolerant invertebrate, we used the fluorescent dyes JC-1 and TMRM to determine the effect of sulfide exposure on mitochondrial depolarization in erythrocytes from the annelid Glycera dibranchiata. In erythrocytes exposed to 0.11-1.9 mmol l-1 sulfide for 1 h, the dyes showed fluorescence changes consistent with sulfide-induced mitochondrial depolarization. At the highest sulfide concentration, the extent of depolarization was equivalent to that caused by the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Even when induced by as little as 0.3 mmol l-1 sulfide, the depolarization was not reversible over a subsequent 5 h recovery period. The mechanism of toxicity was likely not via inhibition of cytochrome c oxidase (COX),since other COX inhibitors and other mitochondrial electron transport chain inhibitors did not produce similar effects. Furthermore, pharmacological inhibition of the mitochondrial permeability transition pore failed to prevent sulfide-induced depolarization. Finally, increased oxidation of the free radical indicators H2DCFDA and MitoSOX™ in erythrocytes exposed to sulfide suggests that sulfide oxidation increased oxidative stress and superoxide production, respectively. Together, these results indicate that sulfide exposure causes mitochondrial depolarization in cells of a sulfide-tolerant annelid, and that this effect, which differs from the actions of other COX inhibitors, may be via increased free radical damage.

Sodium nitroprusside potentiates hydrogen-sulfide-induced contractions in body wall muscle from a marine worm

Hydrogen sulfide (H2S) at concentrations of about 0.05 to 1 mmol.l(-1) appears to function as a gasotransmitter in vertebrates, analogous to nitric oxide (NO) and carbon monoxide, but the actions of H2S in invertebrate tissue have not been well studied. In this study, we investigated the role of H2S in modulating body wall muscle tone in the marine echiuran worm Urechis caupo (Echiuridae). We first determined that U. caupo body wall homogenates produce H2S upon addition of L-cysteine and pyridoxal-5'-phosphate (PLP), and that the rate is increased by addition of 2-mercaptoethanol, suggesting the presence of an activated L-serine sulfhydrase pathway. We then measured the contractile response of U. caupo body wall circular muscle strips to sodium hydrosulfide (NaHS)--which produces H2S in solution--and the NO donor sodium nitroprusside (SNP), both with and without subsequent application of acetylcholine (ACh). We found that NaHS alone stimulated contraction in muscle strips equivalent to about one-third the force of ACh alone, whereas SNP alone had no effect on muscle tone. However, simultaneous addition of NaHS with SNP elicited a much stronger contraction, reaching more than twice that of ACh alone, which could be increased further by subsequent application of ACh.